Polycystic kidney disease (PKD) is a genetic disorder that affects 400,000 to 600,000 persons in the United States; thus the disease is more common than sickle cell disease and cystic fibrosis. PKD is characterized by the development of fluid-filled, epithelial-lined cysts in the kidneys. Nearly 50% of affected persons suffer renal failure making the disease costly not only in terms of dialysis and transplant treatment but also in terms of emotional trauma to patients and their families. The primary goal of this proposal is to advance our understanding of the pathogenesis of PKD by investigating the role of c-myc and SV40 large T antigen gene products in kidney cyst formation. It is now known that during cyst development there are profound changes in gene expression. The endogenous c-myc gene is one of the genes found to be abnormally expressed in the kidneys of the cpk mouse. Further demonstrating the importance of the c-myc gene to cystic disease, was the development of two transgenic mouse models that carry the c-myc or SV40 large T antigen gene. The transgenic mice develop renal cysts analogous to those of PKD. The role of c-myc and SV40 large T antigen genes in cyst initiation and development will be studied by developing a tissue culture model in which these genes will be used to immortalize and establish kidney epithelial cell lines. The c-myc and SV40 large T antigen genes are known to immortalize cells in culture. In addition, they have also been shown to affect gene expression in other cell types. cDNA libraries will be constructed with mRNAs whose levels are altered by expression of the c-myc of SV40 large T antigen gene in the established kidney epithelial cells. These clones will be screened for possible involvement in cyst formation, by examining their expression in the cystic kidneys of cpk mice. Those cellular genes that respond to c-myc or SV40 large T antigen AND that are abnormally expressed in the C57BL/6J-cpk model are prime candidates for genes important to the pathogenesis of polycystic kidney disease. Several observations indicate that tumor and cyst formation may be related. In human PKD, renal micropolyps and adenocarcinomas are found in addition to cysts. The kidney pathology seen in the transgenic mice demonstrates that tumor and cyst formation can be caused by the same etiologic agent. Normal and cystic epithelial cell lines, immortalized with c-myc and SV40 large T antigen gene constructs, will be utilized to determine whether tumor and cyst formation might be a part of the same pathological process. These cell lines will be assayed for transformation by observing growth characteristics and changes in morphology, by determining the cell's ability to form foci in soft agar, and by their ability to form tumors in nude mice. The extent of transformation between the cell lines will be compared to determine whether the immortalized cystic cells have a more aggressive transforming potential than their normal counterparts. If so, this will establish that the cpk gene defect may be on the pathway to transformation.